/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.mapred;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableUtils;

/**
 * A generic directive from the {@link org.apache.hadoop.mapred.JobTracker} to
 * the {@link org.apache.hadoop.mapred.TaskTracker} to take some 'action'.
 * 
 */
abstract class TaskTrackerAction implements Writable {

	/**
	 * Ennumeration of various 'actions' that the {@link JobTracker} directs the
	 * {@link TaskTracker} to perform periodically.
	 * 
	 */
	public static enum ActionType {
		/** Launch a new task. */
		LAUNCH_TASK,

		/** Kill a task. */
		KILL_TASK,

		/** Kill any tasks of this job and cleanup. */
		KILL_JOB,

		/** Reinitialize the tasktracker. */
		REINIT_TRACKER,

		/** Ask a task to save its output. */
		COMMIT_TASK,
		/** 向已有的reduce中添加新的partition */
		ADD_PARTITION
	};

	/**
	 * A factory-method to create objects of given {@link ActionType}.
	 * 
	 * @param actionType
	 *            the {@link ActionType} of object to create.
	 * @return an object of {@link ActionType}.
	 */
	public static TaskTrackerAction createAction(ActionType actionType) {
		TaskTrackerAction action = null;

		switch (actionType) {
		case LAUNCH_TASK: {
			action = new LaunchTaskAction();
		}
			break;
		case KILL_TASK: {
			action = new KillTaskAction();
		}
			break;
		case KILL_JOB: {
			action = new KillJobAction();
		}
			break;
		case REINIT_TRACKER: {
			action = new ReinitTrackerAction();
		}
			break;
		case COMMIT_TASK: {
			action = new CommitTaskAction();
		}
			break;
		case ADD_PARTITION: {
			action = new AddPartitionAction();
		}
			break;
		}

		return action;
	}

	private ActionType actionType;

	protected TaskTrackerAction(ActionType actionType) {
		this.actionType = actionType;
	}

	/**
	 * Return the {@link ActionType}.
	 * 
	 * @return the {@link ActionType}.
	 */
	ActionType getActionId() {
		return actionType;
	}

	public void write(DataOutput out) throws IOException {
		WritableUtils.writeEnum(out, actionType);
	}

	public void readFields(DataInput in) throws IOException {
		actionType = WritableUtils.readEnum(in, ActionType.class);
	}
}
